A conventional foldable umbrella is provided with a coin spring around a shaft above a runner, which is also around the shaft. A middle joint is provided above the coin spring. As the umbrella is folded, the coin spring will be tensioned to provide a force for automatic opening of the umbrella. Since the runner and the middle joint are manufactured independently and connected by the coin spring, they add inconvenience to production and assembly. Moreover, everyone, including the old and the young will not be able to easily operate the umbrella given the high elastic strength of the coin spring.
Accordingly, a primary object of the invention is to provide an inventive structure for automatically opening an umbrella, which includes a single runner with a middle connector and a lower connector and a spring connected between the lower connector and the main rib of an umbrella frame. Now the features and advantages of the present invention will be described in detail with reference to the accompanying drawings.